DESCRIPTION: The objective of the experiments proposed in this application are to identify and functionally characterize the structural proteins that comprise the spindle matrix through the following specific aims: l. Using a cell-free mitotic aster assembly system that is highly enriched in the components of the mitotic spindle matrix, the investigator will prepare antibodies that specifically recognize the three major proteins of the mitotic spindle matrix. 2. Using the antibodies prepared in Specific Aim l, the investigator will use immunodepletion and microinjection to determine if each of these proteins is required for the assembly of the mitotic spindle. 3. Using the antibodies prepared in Specific Aim l, he will isolate cDNA clones encoding each of these proteins of the mitotic spindle matrix and determine their primary amino acid sequence.